Liquid phase sintered molybdenum base alloys

ABSTRACT

A MOLYBDENUM BASE ALLOY CONTAINING AT LEAST TWO METALLIC ELEMENTS WHICH FORM AN ALLOY WHICH MELTS AT A TEMPERATURE CONSIDERABLY BELOW THAT OF MOLYBDENUM AND WHEN IN THE MOLTEN STATE DISSOLVES APPRECIABLE MOLYBDENUM DURING LIQUID PHASE SINTERING AND WHICH MAY BE SHAPED BEFORE OR AFTER SINTERING FOR EXAMPLE, BY MACHINING, TO FORM DESIRED SHAPES SUCH AS HOT MELT FORMING TOOLS SUCH AS DIE CASTING DIES, CORES, ETC., THUS AVOIDING EXPENSIVE HOT WORKING AND/OR HOT FORGING IS DESCRIBED.

3,720,990 LIQUID PHASE SINTERED MOLYBDENUM BASE ALLOYS Earl I. Larsen, Indianapolis, Ind., assignor to P. R. Mallory 8: Co. Inc., Indianapolis, Ind. No Drawing. Filed Jan. 13, 1969, Ser. No. 790,861

Int. Cl. 1322f 3/00 US. Cl. 29182 18 Claims ABSTRACT OF THE DISCLOSURE Tungsten and tungsten base alloys have advantages over currently used tool steel materials for die casting dies and their components for the casting of high temperature molten materials such as copper, brasses and bronzes.

While the foregoing tungsten base materials perform extremely well, they have certain undesirable economic characteristics. Tungsten is quite expensive on a weight basis. Its density of 19.3 g./cc. is one of the, highest of all elements. Therefore, its volume per unit weight is lower than most other metallic elements. Consequently, more weight is required to make a given die or tool than if it were fabricated from most other metals.

Molybdenum has a density of 10.2 g./cc. which is approximately 52.8% that of tungsten. In other words, almost twice the volume of molybdenum can be had for the same weight. Since molybdenum is normally considerably less costly than tungsten, the economic advantages of molybdenum over that of tungsten are further increased. Furthermore, molybdenum is a refractory metal and has a high melting point; both of which make it attractive as a potential material for die casting dies, cores and other mold components.

It is known that wrought molybdenum and more particularly molybdenum with minor (less than 1%) percentages of such cements as titanium and zirconium perform extremely well as die casting dies, core rods, and other parts of molds in the die casting of high temperature alloys such as yellow brass.

At the present, such molybdenum alloys are generally fabricated by first vacuum melting to form an ingot. The ingot is then hot forged or otherwise worked to form a slab, block, or other shape of suitable size from which a die, core rod, or other mold segment can be machined.

The forging and/ or other working operations may cause the finished die or mold segment to have a perferred grain orientation. Thus, the ductility of the die or mold segment is adversely affected in planes perpendicular to the elongated grain structure. Failure of the aforementioned molybdenum base alloys by cracking and spalling along these planes results.

United States Patent 3,720,990 Patented Mar. 20, 1973 The melting, casting, and subsequent hot forging or working increases the cost of the final article a great deal. Thus, the fundamental economics of lower density, greater volume per unit of weight, and lower cost of molybdenum are often offset, it not completely eliminated by these expensive procedures.

It is therefore an object of the present invention to develop a new series of molybdenum base alloys or composites for all types of applications and especially those for dies, cores, core rods, or other mold segments for the high temperature forming of metals such as the die casting of copper, brasses, bronzes, steel and other metals and alloys.

It is another object of the present invention to utilize the economic advantages of molybdenum resulting from its relatively low density, volume per unit of weight, and relatively low cost to form articles which will have long life and be reasonably inexpensive.

It is another object of the present invention to use powder metallurgy techniques to form molybdenum alloys or composites having the necessary properties to form dies, core rods, mold segments, etc.

Another objective of the present invention is to utilize liquid phase sintering in the fabrication of the molybdenum base alloys or composites made from metal powders.

Another objective of this invention is to provide a molybdenum base alloy or composite free from any preferred grain orientation so that it will have substantially the same mechanical properties in all planes.

Other objects will be apparent from the following description.

The alloys or composites of the present invention are composed of at least three metallic elements with molybdenum being the base or predominant element. To be effective as an alloy or composite for use in die casting dies, core rods, or other components of dies or molds used to shape or form high temperature molten metals, the molybdenum content of the alloy should be at least about by weight.

The other two or more elements form an alloy which when molten will dissolve an appreciable quantity of molybdenum to bring about liquid phase sintering.

The amount of molybdenum which will be dissoved by the additional metallic elements which form the dissolving alloy is dependent on several factors:

( l) The molybdenum content, and conversely the amount of dissolving alloy present;

(2) The composition of the dissolving alloy; and

(3) The liquid phase sintering temperature.

To attempt to place actual numbers on the three foregoing variables is extremely diflicult. For example, the amount of molybdenum dissolved in a ternary composite containing 99 percent molybdenum would be entirely different than one containing 80 percent molybdenum.

In view of this, it is estimated that the amount of molybdenum dissolved in a composite containing 99 percent molybdenum would be on the order of .5 to 1.5 percent, and that of an 80 percent molybdenum composite might range from 20 percent to about 30 percent.

The following are the weight percentage compositions of the alloys which will bring about liquid phase sintering of the alloy or composite.

The total weight of the alloying elements will be present in the molybdenum base in amounts up to about 20%, with molybdenum making up essentially the balance.

TABLE Mo Alloy content, content, percent percent Alloy composition (1) 20-1 2%8% B-l-bal. essentially Co. (2) 20-1 2%10% B+bal. essentially Fe,

+ 20-1 2%20% B |-bal. essentially N1. 20-1 1%20% B+bal. essentially Ob and/or Ta. 201 1%20% B-i-bal. essentially Cr. 20-1 1%l0% B-i-bal. essentailly V. 20-1 10%70% Mn+bal. essentially N1. 20-1 30%90% Mn+bal. essentially Fe. 20-1 20%,-70% Mn+bal. essentially u. 20-1 30%-90% Mn+bal. essentially Ti. 20-1 57%80% Mn+bal. essentially r. (12)..- 80-99 20-1 30%90% Mn+bal. essentially U. (1 80-99 20-1 20%,-95% Mn+bal. essentially l. 20-1 20%,-80% Mn+bal. essentially o. 20-1 20%80% V+bal. essentially Fe. 20-1 20%,-60% V+ba1. essentially Ni. 20-1 l%70% V-I-bal. essentially Co. 20-1 %30% V+bal. essentially Mn. -1 5%50% Si-l-bal. essentially Ni. 20-1 5%65% Si-l-bal. essentially Fe. 20-1 5%70% Si-I-bal. essentially Co. 20-1 5%-30% Si+bal. essentially Cu. 20-1 5%-60% Si+bal. essentially V.

In the table, the percentages for the tWo' or more elements other than molybdenum total 100% in each instance. For example in item No. 1 the compositions might be:

80% Mo-20% (2% boron-98% cobalt) 80% Mo-20% (8% boron-92% cobalt) 90% Mo-10% (2% boron-98% cobalt) 90% Mo-10% (8% boron-92% cobalt) The other compositions shown in the table may vary in the same way.

Additional alloying elements may also be added to the alloys of the present invention for particuar applications including for example hardening elements, by those skilled in the art.

The shapes can be formed from powders of the foregoing alloys in one of the following ways:

An alloy having a composition in the table may be pressed to a given shape, machined to the particular shape desired, and then sintered to form a composite alloy. Additional machining and/ or grinding may then be carried out if necessary or desirable.

Alternatively, the alloy may be first pressed and then sintered, in which case machining and/or grinding is carried out at the end of the operation. As will be apparent to those skilled in the art, close tolerances may be obtained according to either of these procedures.

The metal powders may be pressed either as alloys containing the metals listed in the table or as elemental powders of the metals listed in the table or as mixtures of both.

In the pressing operation, any of the Well known binders may be used, for example zinc stearate and/or parafiin. Alternatively, bonding processes may be carried out in which no binder is needed. For example, the isotactic bonding particles to be pressed together are placed in a plastic bag and liquid pressures of at least about 10,000 p.s.i. are applied to the particles through the bag to bind the particles together.

The sintering temperature to be used in processing the alloy of the present invention is from about 1000 to about 1600 C. An optional pre-sinter may be utilized in which a temperature range of about 300 to 1000 C. is used for the pre-sintering operation.

In both the pre-sintering and the sintering operation an atmosphere which excludes oxygen must be maintained. Such an atmosphere may be maintained by means of a vacuum or by means of non-oxidizing gas such as hydrogen, nitrogen, argon, helium, etc. Additionally, an atmosphere of dissociated ammonia may be used as the sintering atmosphere.

The alloys of the present invention may be used as dies, core rods and other mold parts, in the casting of copper and copper base alloys such as brasses and bronzes, other high melting point metals including iron, nickel and cobalt base alloys, as well, and in the casting lower temperature metals including aluminum and its alloys and magnesium and its alloys.

The properties of the alloys of the present invention are generally in the same range of those of commercially pure molybdenum, although some have considerably greater strengths at both room and elevated temperature.

I claim:

1. A liquid phase sintered molybdenum base alloy consisting essentially of:

at least about by weight molybdenum; and

at least two additional metallic elements said additional metallic element forming an alloy which when molten which will dissolve an appreciable amount of molybdenum;

said additional metallic elements being selected from one of the following groups:

(A) manganese and at least one additional element selected from nickel, iron, copper, titanium, zirconium, uranium, silicon, cobalt and mixtures thereof; the manganese content of said additional metallic elements ranging from about 10 to about the weight of said additional metallic elements;

(B) vanadium and at least one additional element selected from the group consisting of iron, nickel, cobalt, managanese and mixtures thereof, the vanadium content of said additional metallic elements ranging from about 5 to about 80% of the weight of said additional metallic elements;

(C) silicon and at least one additional element selected from the group consisting of nickel, iron, cobalt, vanadium and mixtures thereof, the silicon content of said additional metallic elements ranging from about 5 to about 70% of the weight of said additional metallic elements;

(D) boron and columbium.

2. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 10%-70% manganese with the balance essentially nickel.

3. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 30%90% manganese and with the balance essentially iron.

4. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 20%70% manganese with the balance essentially copper.

5. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 30%-90% with the balance essentially titanium.

6. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 5%80% managanese with the balance essentially zirconium.

7. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 30%90% managanese with the balance essentially uranium.

8. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 20%-95% manganese with the balance essentially silicon.

9. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 20%-80% manganese with the balance essentially cobalt.

10. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 20%-80% vanadium with the balance essentially iron.

11. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 20%60% vanadium with the balance essentially nickel.

12. An alloy according to claim 1 wherein said additional metallic elements consist essentially of l0%-70% vanadium with the balance essentially cobalt.

13. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 5%-30% vanadium with the balance essentially manganese.

14. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 5%50% silicon with the balance essential nickel.

15. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 5%65% silicon with the balance essentially iron.

16. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 5%70% silicon with the balance essentially cobalt.

17. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 5%-60% silicon with the balance essentially vanadium.

18. An alloy according to claim 1 wherein said additional metallic elements consist essentially of 1%20% boron with the balance essentially eolumbium.

5 References Cited UNITED STATES PATENTS 1,807,581 6/1931 Bates 75l76 2,179,836 11/1939 Wisler 75-176 10 CARL D. QUARFORTH, Primary Examiner R. L. TATE, Assistant Examiner US. Cl. X.R. 15 75122.5, 176 

